Producing and/or finishing screw threads by grinding



Nov. 29', 1938. s, J, HARLEY I 2,138,739-

PRODUCING AND/OR FINISHING SCREW THREADS BY GRINDING Filed Nov. 21, 19ss Patented Nov. 29, 1938 UNITED STATES PROlJUCING AND/OB FINISHING SCREW THREADS BY GRINDING Stanley Jaifa Harley, Stivlchall, Coventry, E gland Application November 21, 1935, Serial No. 50,948 In Great Britain November 23, 1934 2 Claims.

This invention relates to the production and/or finishing of threaded members, such as taps, screw thread chasers and similar continuous or repeated forms by means of a rotating grinding wheel having a plurality of annular grinding serrations or cutting edges, the diameters of which vary progressively from one edge of the wheel to the other.

I am aware that a method of grinding threaded members of the kind referred to has already been proposed, in which the wheel is used with the serrations of progressively increasing diameter, that is to say, with the smallest diameter as the leading edge, so as simultaneously to grind a plurality of convolutions of the thread to difierent sizes, and to successively operate upon each convolution to grind successive increments therefrom to reduce the convolutions successively to uniform size. the wheel all the cutting edges or serrations'are in use during each grinding operation and con sequently frequent redressings of the wheel become necessary.

The object of the present invention is to pro; long the useful life of wheels of the kind referred to by using the wheel in such a manner that as the leading serrations become worn new serrations can be successively brought into effective operation on the work by relative adjustment between the wheel and the work in a radial direction.

For this purpose according to the present invention the wheel is used with the largest diameter as the leading edge that is to say, with the diameters of the serrations in aprogressively diminishing order.

The above described mode of using the wheel also has the further advantage that since only a relatively small number of serrations or cutting edges are in operation at a time there is not the same tendency for the work to become overheated and softened as where the whole or a greater part of the serrations on'the wheel are I in active operation on the work at the same time.

In the accompanying drawing,

Figure 1 is a plan view of a grinding machine having the grinding wheel arranged andoperating according to my invention.

Figure 2 is a magnified detail sectional view illustrating the manner in which the grinding wheel operates upon the work.

The mode of using grinding wheels of the kind herein referred to according to the present invention can be employed in any appropriate type of grinding machine in which provision is made With this method of using,

for relative axial movement between the wheel and the work. The machine shown in Figure 1 is thereforeto be regarded as an example only and is not to be construed as limiting the scope of the invention. In this particular machine 5 the grinding wheel a is rotatably mounted in a head I) secured to a transverse slide 0 whilethe work d is mounted between head and tail stocks e and I carried by a longitudinal slide g. The two slides are guided in ways on the bed of 10 the machine and can be moved either by hand or power.'

During the grinding operation the wheel a is rotated at a high speed but is axially fixed. The work is rotated at a comparatively low speed and is given an axial movement at the same time the two movements being related so that the annular serrations on the wheel produce or follow the. threads in or on the work to grind out the metal therefrom or to re-surface or finish an existing thread as the case may be. The slide carrying the grinding wheel head is adapted to be moved to bring the wheel into and out of engagement with the work and to regulate the depth of cut as by means of the screw and hand wheel.

As will be seen the grinding wheel is arranged with thelargest diameter as the leading edge so that the serrations or cutting edges a are oi successively diminishing diameter. As the work is traversed across the wheel in the direction indicated by the arrow the wear is at first taken wholly by the leading serrations the maximum wear falling upon the serration having the largest diameter, while the serrations at the trailing end of the wheel are not at first subject -to any wear. As the leading serrations become worn and ineffective to produce the full thread form in the work the feed of the wheel towards the work brings the partly worn and unwom serrations successively into operation. In this 40 way the'useful life of the wheel between dressings is considerably increased.

I claim:-

1. A grinding machine comprising a work carrier and a grinding wheel having at least one large diameter leading serration adapted to operatively engage the work, and a series of smaller diameter annular serrations progressively in diameter from the leading serrations, each said serration being adapted to operatively engage the work only when the preceding serration has become worn, and means for causing relative axial movement between said wheel and work carrier in such a direction that the serrations of the wheel approach the work piece F in order of the size of their diameters, with the large diameter leading serration first approaching and operatively engaging the work piece.

2. A grinding machine comprising a work carrier and a grinding wheel having at least one large diameter leading serration adapted to operatively engage the work, and a series of smaller diameter annular serrations diminishing progressively in diameter from the leading serrations, each said serration being adapted to operatively engage the work only when the preceding serration has become worn, means for causing relative axial movement between said wheel and work carrier in such a. direction that the serra-,

tions of the wheel approach the workpiece in order of the size of their diameters, with the large diameter leading serration firstapproaching and operatively engaging the work piece, and means of relative radial adjustment between said wheel and work carrier. 

